the end of the pipe, opens the throttle-valve, pass directly aft in a column of the precise which admits it into the next length of piping, diameter of the tube. Mr. Smith has tried the so that the train may proceed from one station effect of the tube, and finds the common to another without stopping. The tractive force principle the best. The most extraordinary is thus evidently derived partly from the effect of the screw as a propeller, has yet to be pressure of the atmosphere on the piston; its discovered, viz., that with the proportions amount will depend on the area of the piston, before named, it moves the vessel through the and on the extent to which the exhaustion of water as fast as if it were working in a solid. the air can be carried by the air-pump; there- The cause of this anomaly, probably, is, that fore the difficulty of keeping the pipe air-tight as the vessel passes through, the water closes increases with its length, and with the pressure in as fast as the vessel goes, to fill up the obtained. The tube on the branch of the vacuous space that must otherwise be left; in Birmingham, Bristol, and Thames Junction doing this, the water apparently impinges upon Railway, where this system has been in the plunges of the screw, so as to oppose a operation for more than five years, is nine greater resistance to its backward stroke, than inches internal diameter, and but half a mile if it were placed over the ship's side in a long. It is on an incline of part 1 in 120, and position similar to that of the paddle-wheel. part 1 in 115. A vacuum equal in some This closing in of the water produces a current instances to a column of mercury 234 inches following the ship, but whether this current is high has been obtained, and loads of thirteen chiefly due to the particular form of the vessel, tons have been propelled at a speed of twenty or to the capillary attraction of its bottom, is a miles an hour. On the Dalkey branch of the problem. When the vessel is moved, the Dublin and Kingstown Railway, the tube is engine always makes full two-thirds the fifteen inches in diameter, and the length is number of strokes it makes when the vessel is one mile and a quarter. The average incline under weigh; and when under weigh, the boat is 1 in 100. The exhaustion has been ex-almost invariably travels as fast through the tended to 22 inches of mercury; and three carriages loaded with passengers have been propelled up the incline, at the rate of forty miles an hour. We have frequently travelled on the Croydon line with two carriages at the speed of eighty miles an hour, with the mercury at 23.”

water, as if the screw were working in a solid. Having stated that the water is thrown back two-thirds of the rate when at moorings, the remaining one-third may be imparted to the vessel when moving; so that, if the current be flowing only at the rate of six miles an hour, the effect of nine miles an hour may be proWith regard to the Electric Printing Tele-two-thirds, or six miles, for actual slip.” duced upon the vessel, allowing the remaining graph, our author conveys some very valuable information, but as our space is limited, we will pass on to an account of the action of the Screw-Propeller :

In taking leave of Mr. Portwine's book, we cannot but compliment him on the success of his exertions, to place within the reach of all, a popular treatise on the Steam-Engine, the Atmospheric Railway, the Electric Telegraph, and the Screw-Propeller, and sincerely trust that an infinitive number of editions will be

"It is difficult to ascertain precisely in what way the water is acted on by the screw, when the vessel is moving rapidly through that element; but from close observation, with models in a glass trough, Mr. Smith has found the reward of his labours. that the water partakes but very little of the rotative motion of the screw, but is drawn on all sides from the circumference towards the

a

centre, and, as soon as it gets within its influence, is immediately thrown aft in column, not exactly parallel, but more in the form of an inverted cone, the apex of which is in proportion to the diameter of the screw; occasioned probably by the disposition bodies have to fly off from the object on which they impinge, at an angle equal to the angle of incidence. The screw, therefore, in its entire form, would produce this kind of action from the circumstance that, if right angles were drawn from every part of it, a focus, similar to that alluded to, would be produced. When the screw has been working, when the vessel is moved, the current of water which is thrown back, assumes the form of an inverted cone. A similar effect is produced when the vessel is in motion. It may, therefore, be inferred, that the action of the screw, in the uncovered condition, is different to what it would be if the screw were enclosed, the supply of water would require to enter at the end of the screw instead of the sides, and flying off, it would

THE IRON TRADE IN FRANCE.--The Moni

teur contains the following data on the produce and manufacture of iron in France :

"There is not," it says, "a branch of industry
more labourers than that of
occupying
iron. The number engaged in the mines and
works are estimated at 51,000. The other indi-
viduals employed in carrying the metal, and in
various external works, being as numerous,
the iron industry affords labour to at least
100,000 men. The produce in 1845 exceeded
166,000,000 francs. To that human force must
be added, 2,047 hydraulic-engines, and 207
steam-engines, representing together a power
equal to that of 26,504 horses. The number of
steam-engines was only 109 in 1840, so that it
nearly doubled in five years.

PHOSPHORESCENCE OF THE RIVER WYE.-A curious phenomenon hitherto unobserved in rivers, has been perceived in the Wye; this is no other than that luminous appearance denominated phosphorescence. An amusing anecdote is related concerning it: An old inhabitant of a cottage near the celebrated abbey ruins

ANSWERS TO QUERIES. BURNED CLAY.-Sir,-Presuming that " L. G. L." refers to the method of preparing clay for crucibles, I beg to state that Brande, in page 1036, vol. ii. of his "Manual," recommends a composition of one part of pure clay, mixed with about three parts of coarse and pure sand, slowly dried and annealed. This will resist a very high temperature without fusion, and generally retain metallic substances. Yours truly, MARTIN JONES. Chelsea, October 15, 1847.

PAINTED WALLS.-Sir,-"A Constant Reader" has inquired respecting the cause of "Roman cement eating through painted walls," but I should surmise that he means the cause of the paint stripping off walls formed of]

Bain's Electric Clock.

pushes the sliding-bar off the gold stud on to the agate, which, being a non-conductor of electricity, the current is cut off, and the coil is no longer a magnet; therefore the permanent] momentum carries it back; but, in falling back, the pin on the pendulum-rod again pushes the slide on to the gold stud, and the coils once more become magnets; and thus the motion of the pendulum is continued, and which pendulum gives motion to the clock by a very simple propelling apparatus.

THE electric clock is worked by a galvanic bat-coils have no effect on the magnet, and its own tery of low power, placed in the earth: two holes are dug at a few feet from each other; into one is put a quantity of common coke, such as is used in the locomotive engines, and in the other is placed a plate of zinc, about two feet square and one eighth of an inch in thickness; from each of these substances a wire is brought up to the clock, taking care that they are well insulated from each other.chanism presents the nearest approach that This arrangement, simple as it may appear, forms the galvanic battery, which, according to the inventor's statement, will continue to produce a constant current for a period of many

years.

This power is applied to work the clock by; one pole of the battery being connected by means of a wire with a brass bracket on the right of the clock (as you face it), and on the left is a bracket of similar appearance. The one on the right has a surface of gold, and the one on the left an agate surface, in the centre of which agate is inserted a stud of gold, the top of which is level with the surface of the agate. These brackets give the clock a very elegant and handsome appearance.

This simple but very beautiful piece of me

has yet been made to the long-sought-for perpetual motion, for, according to the inventor's statement, if a solid three feet cube of zinc and a corresponding surface of copper (not necessarily solid), were placed at a considerable depth in the ground and some distance from each other, and joined by a strong wire well insulated and protected from moisture, it would constitute a source of electricity which would last several hundred years.

These clocks may be worked simultaneously throughout a house or town, or even through| the whole country where wires are laid down for the purpose, so that Greenwich time might be shown in every locality throughout the country at the same moment. This is simply to have a pendulum set in motion by the electric current, which being once regulated would, by a quantity of wires, set in motion any number of clocks (no matter where situated), and thus give the exact time of the dial from which the current of electricity sprung.

Travelling on the surface of the two brackets is a steel slide, and from the bracket on the right being in connection with a pole of the battery, and the steel slide being a conductor, when the end of the slide is on the gold stud in the agate surface, the current of electricity necessarily passes along it, the gold stud being in connection with a wire carried up to the VENTILATION BY JET OF STEAM.-At the top of the pendulum. The ball of the pendulum is composed of a helix or coil of insulated Polytechnic Institution, Dr. Bachhoffner is now copper wire enclosed in a brass cylinder, the illustrating the effect of the steam jet for ventwo ends of which wire are brought up to the tilation, used in the new House of Lords,— back of the pendulum-rod, and are united to showing how water, in its expanded state, can, two very flexible steel springs by which the by displacing large volumes of air, contribute pendulum is suspended to the top of the clock-to a purpose so desirable as that of renewing case; the wire before mentioned being attached the atmosphere of crowded buildings. to one of the springs allows the current to flow that the plan of ventilating by steam is not of Bachhoffner, by several historical details, proves down into the helix or coil (which it renders magnetic), returning up through the other wire to the opposite suspension spring, and thence by a wire to the earth, thus completing the electric circuit. Fixed to the back of the case are two coils connecting with each other, and in the bob of the pendulum the steel magnets are so placed that the north poles are opposite each other, the opening in the coils being sufficiently large to allow the bob of the pendulum to vibrate without touching them.

Our numerous scientific readers are aware that it is a law in magnetism that similar poles will always repel, while on the other hand dissimilar poles will always attract, each other; and as the helix, being magnetised, must have a north and south pole, it results that the north pole of the magnet is repelled by the north pole of one of the permanent stationary coils, while, at the same time, the south pole of the magnet is attracted by the north pole of the other stationary coil. This has the effect of giving motion to the pendulum, but, on this motion being given, a pin on the pendulum

Dr.

a date so recent as many imagined, but was brought before the world in the year 1794. In order to show the displacement of air by steam, the lecturer has a most complete set of mechanical apparatus, and, aided by the enormous hydro-machine of the institution, the results exhibited was the drawing, with produces some astonishing effects. Among immense velocity, of solid bodies, such as eggs and paper, through an iron tube, at the upper part of which a jet of steam was allowed to pass, while pieces of pasteboard and tin were, by the force of the external air, brought into such close contact with the orifice, that considerable force was required for their removal.

TO MAKE BRASS.-Place in an earthern crucible a portion of copper filings, mixed with about twice its quantity of finely granulated zinc; cover the whole with charcoal powder, press it well together, and then expose it to the action of a clear fire for some time;-the two metals will then combine and form brass.

Murdock's Emprovements in the

PREPARATION AND EMPLOYMENT OF CERTAIN
COLOURS AND MATERIALS FOR PAINTING.

THIS Communicated invention, enrolled September 10th, 1847, consists in substituting the ordinary compounds of lead and copper at present in use, by certain substances unacted upon by sulphuretted hydrogen as pigments or paints, particularly as regards the greens, yellows, and reds. The following are the processes with reference to the preparation of the colours, as described by the patentee.

sulphuretted hydrogen passed through it. The sulphuretted hydrogen may be that evolved in forming a second solution of the native sulphuret. The tube by which the gas is conducted into the solution should be of glass, and wide enough to prevent its clogging: the vessel should be covered, and the gas made to pass through a series of vessels, and at last conducted into a vessel of milk of lime; during the process the solution should be stirred occasionally with a wooden spatula. The precipitate is to be washed thoroughly, and dried at a temperature of from 100 degrees to 120 degrees; at a higher temperature than this the hydrated sulphuret would close its combined water and become black. To form the zinc green, the patentee dissolves in hot Zinc Yellows.-This process is divided into water 49lbs. of pure dry sulphate of cobalt, three parts. By the first he obtains what he and to this adds 255lbs. of oxide of zinc slaked calls marigold yellow. For this purpose he with a little water; the whole is then boiled mixes in a boiler 120lbs. of bichromate of to dryness, and heated red-hot in a muffle. potass with from 700 to 800lbs. of water, and The calcined mass must then be cooled and 60lbs. of "zinc white." The boiling is thrown into water, thoroughly washed, and continued for from 24 to 36 hours. The dried. The patentee claims this his process of precipitate is then separated and washed, and neutralising the sulphate of cobalt with oxide the first washings added to the solution from of zinc. The patentee next describes the which it was precipitated. When perfectly process for making a dryer, or drying oil, by washed the precipitate is dried, and either boiling for 6 or 8 hours 200 gallons of purified reduced to powder or made up into cakes. By the second he obtains lemon yellow, by adding to the solution which remains from the first process, together with the washings which were added to it, sulphate of zinc, formed by adding to 75lbs. of oxide of zinc 45lbs. of sulphuric acid of commerce, of specific gravity 634 degrees. This is to be boiled as in the first process, and the precipitate separated, washed, and dried. To the solution remaining from this last process, together with the first washings of the precipitate, he adds sulphate of zinc, formed by adding to 15lbs. of oxide of zinc 7lbs. of sulphuric acid of commerce. This is to be boiled as before, and the precipitate washed and dried. This gives a pale yellow, of a tint between the marigold and citron tint above described. The baryta yellow is formed by adding to a solution containing 100lbs. of chloride of barium, 84lbs. of the double neutral chromate of potass and soda, boiling these together, then separating, washing, and drying the precipitate. From these yellows the patentee says he can obtain any shade of yellow required by adding, if necessary, raw terra sienna, or the antimony red hereafter described. And greens in the same manner may be obtained, of any shade, by adding to the yellows a blue, unacted upon by sulphuretted hydrogen. Antimony red, or orange red, is made by dissolving the native sulphuret of antimony in hydrochloric acid, in such proportion that it will just dissolve the whole of the sulphuret; this proportion the patentee finds to be about 6 of acid to 1 of the native sulphuret. The solution is then filtered, and water or acid is added to it until its specific gravity is between 13 degrees and 17 degrees of the French ariomètre. The patentee prefers 15 degrees, but claims all degrees between 13 degrees and 17 degrees. When the solution has been brought to the above density, it is placed in a suitable vessel, and

linseed oil, and then adding to this 10lbs. of peroxide of manganese in fine powder. The mixture is to be boiled for 5 or 6 hours, and filtered when cool. Peroxide of iron will answer the purpose, but it is not so effective as peroxide of manganese. If desired, the protoxide, sulphate, acetate, or carbonate of manganese may be used. This dryer may be mixed with the paint in the proportion of 1-10th to 1-20th. Instead of the dryer above described, the peroxide of manganese may be ground up with the paint in the same manner that litharge is now employed. It should, in such case, be used in the proportion of 1-10th to 1-25th. In applying his patent colours for: the purpose of polished painting, the patentee lays on, first, several coats of zinc white, and when dry the surface is rubbed down with pumice till it is brought to a dead polish. The colours, whether for marbling, graining, &c., previously mixed with the dryer, are then laid on, and when dry will not require varnish. In applying these colours to paper-hangings no alteration whatever is required to be made in the common process, and for the purpose of satining or watering paper, or enamelled cards, the zinc white is employed instead of the white lead now commonly used.

TO SILVER COPPER.-Precipitate silver from its nitric solution, by the immersion of polished plates of copper. Take of this silver, 20 grains; of supertartrate of potass, 2 drachms; of common salt, 2 drachms; and of aluma drachm; mix the whole well together. Then take the article to be silvered, clean it well, and rub some of the mixture, previously a little moistened, upon its surface; the silvered surface may be polished with a piece of soft leather. The dial-plates of clocks, scales of barometers, &c., are all plated thus.